Permanent magnet erase head



Nov. 7, 1967 J. METZ PERMANENT MAGNET ERASE HEAD Filed Au 12, 1965 INVENTOR JACK L. METZ ATTORNEY United States Patent 3,351,717 PERMANENT MAGNET ERASE HEAD Jack L. Metz, Des Plaines, Ill., assignor t Teletype Corporation, Skokie, 11]., a corporation of Delaware Filed Aug. 12, 1965, Ser. No. 479,105 Claims. (Cl. 179-100.2)

ABSTRACT OF THE DISCLOSURE A permanent magnet erase head for erasing magnetic recording media comprising a pair of pole pieces including inwardly'directed portions positioned in engagement with the recording media and separated by a piece of non-magnetic material and outwardly directed portions extending oppositely from the inwardly directed portions, a U-shaped permanent magnet having poles positioned in engagement with the outwardly directed portions of the pole pieces and mounted for rotation with respect thereto from a position whereat each pole of themagnet individually engages one outwardly directed portion so that a magnetic field is generated across the piece of non-magnetic material to a position whereat each outwardly directed portion engages both poles of themagnet thereby preventing generation of a field across the piece of non-magnetic material and a handle for rotating the permanent magnet.

In magnetic tape systems it frequently becomes desirable to erase from the tape all of the information previously encoded on the various levels or traces of the tape by magnetizing the magnetic material on the. tape in a given direction or polarity. In the past, mechanisms have been provided which include a permanent magnet movable into and .out of proximity to the tape or into and out of closer association with the magnetic gap between pole shoes which serve as an erase head. In such devicesthe magnetic. field atthe gap between the pole shoes of the erase head is reduced when the permanent magnet is 'moved away from the gap 'but is not reduced sufiiciently to remove a'vestigelof erasing efiect at the erase head. i H

It is an object of the presentinventionto provide a simple and highly eifectiveerasefhead for magnetic tape systems. v 7

Another object of the invention is to simplify the construction and mode of operation of a permanent magnet erase head.

;In accordance with a preferred form. of the invention a pair of pole members positioned closely adjacent to a moving tape, having magnetizable material on. it, are suitably spaced apart and are formed with portions which extend away from the tape to a point wherethey engage a permanent magnetof the horseshoe type having its pole extensions spaced apart, a distance corresponding to the spacing of the extensions on the pole membersand having the ends of its pole extensions sufiicie'ntly wide so that when the permanent magnet is'vturned through a 90 a magnetic field at the gap on the pole shoes or members will have each of its pole extensions in intimate contact with both of the extending portions of .the pole-shoes thereby to utilize the pole shoe extensions as keepers or magnetic shunts which substantially completely shunt the permanent magnet and prevents thegeneration of magnetic flux across the gap between the pole shoes.

A more complete understanding of the invention may be had by reference to the accompanying drawing wherein:

angle the pole extensions on it rather than forming "ice f FIG. 1 is a view in perspective of the apparatus comprising the preferred embodiment of the invention, shown in proximity to a magnetic tape, parts being broken away to more clearly disclose 1 the structural features of'othersof the parts of the apparatus;

FIG. 2 is a view also in perspective of the permanent magnet and pole shoes with its supporting structure completely eliminated; and

FIG. 3 is an enlarged transverse sectional view taken substantially along line 3-3 of.FIG. l'in the direction of the arrows.

In the drawing wherein like reference numerals designate the same parts in the several views, a supporting structure 10 is shown mounted in position to maintain a pair of pole pieces 11 and 12 in close proximity to a moving length of magnetic tape 13. The pole pieces 11 and 12 are made of soft iron and have inwardly directed reduced portions 14 and 15 between which there is positioned a piece of nonmagnetic material 16 to provide a magnetic gap between the portions 14 and 15. The pole pieces 11 and 12 are bent back to form diverging portions 17 and 18 which are integral with web portions 19 and 20. Extending from the web portions 19 and 20 and at right angles thereto are a pair of extensions 21 and 22. The extensions 21 and 22 are suitably fixed in a supporting structure 10 is in the form of a hollow, box-like structure having a slot 23 formed in it through which the webs 19 and 20 extend. In its side 24 the supporting structure rotatably supports a shaft 25 of nonmagnetic material. The supporting structure 10 is also of nonmagnetic material. The shaft 25 carries a permanent magnet26 which is in elfect asubstantially U-shaped or horseshoe magnet of generally cylindrical configuration having a pair of pole extensions 27 and 28 formed by cutting a slot 29 through the body of the permanent I magnet 26. A bushing 30 serves to rotatably support the shaft 25 which is provided with a handle or lever 31 for manipulating it.

As shown in FIG. 1, the permanent magnet has been rotated by means of the, handle 31 to a position where its pole extensions, similar to the legs of a horseshoe type magnet,- areinrintimate contactindividually with the extensions 21 and22, the pole extension 27'being in engagement with the extension 21 of the pole piece 11 and the pole extension 28 being in intimate contact with the surface of the extension v 22 of the 'pole piece 12. With the permanent magnet 26 rotated to this positiona flux field ofhigh intensity is generated at the gap between the reduced portions 14 and 15 and when magnetic tape 13 is moved past this gap it ismagnetized in a given direction to effectively erase any information which had been stored in, the tape by the previous magnetization of portions of the tape in the opposite direction.

' .When it is desired to disable the erase head mechanism, the permanentmagnet 26 need only be turned to the position shown in FIG. 2 where its pole extension 27 engages a substantial portion of the extensions 21 and 22 of the pole pieces 11 and 12 and its pole extension 28-also engages a substantial portion ofthe extensionjZl and 22 on the pole pieces 11 and 12. When the permanent magnet .26 is in the position shown in FIG. 2 it has its magnetic field shunted since the extensions 21 and 22 serve askeepe ers interconnecting the pole extensions 27 and 28 of the permanent'm'agnet 26. A U 7 Although a particular embodiment of the invention is shown in the drawings and described in the foregoing specification, it will modification and rearrangement, and substitution of parts be understood that the invention is not limited to that specificembodiment, but is capable of 3 What is claimed is: 1. A permanent magnet erase head for magnetlc recording systems comprising:

a pair of pole shoes of magnetic material;

means for supporting said pole shoes in closely spaced juxtaposition to form a flux concentrating gap between them adjacent the path of movement of a magnetic recording medium;

extensions on said pole shoes spaced an appreciably greater distance than the width of the flux concentrats p;

a permanent magnet having pole extensions of opposite polarity spaced substantially the same distance apart as the spacing of the pole shoe extensions; and

means for supporting said permanent magnet for rotation from a position where its pole extensions will individually engage the pole shoe extensions to generate a flux field at the pole shoe gap, to a position Where both of its pole extensions will bridge the pole shoe extensions and shunt the magnetic field at the gap.

2. A permanent magnet erase head for magnetic recording tape systems comprising:

a pair of pole shoes of magnetic material;

means for supporting said pole shoes in closely spaced juxtaposition to form a fl-ux concentrating gap between them adjacent the path of movement of a magnetic recording medium;

extensions on said pole shoes spaced an appreciably greater distance than the width of the flux concentrating gap;

a substantially U-shaped permanent magnet having pole extensions of opposite polarity spaced substantially the same distance apart as the spacing of the pole shoe extensions, said permanent magnet pole extensions being of sufliciently wide, in a direction normal to their spacing, to bridge the extensions on the pole shoes; and

means for supporting said permanent magnet for rotation from a position where its pole extensions will individually engage the pole shoe extensions to generate a flux field at the pole shoe gap, to a position where both of its pole extensions will bridge the pole shoe extensions and shunt the magnetic field at the gap.

3. A permanent magnet erase head comprising:

pair of complementary pole'mem-bers of magnetic material each including a shoe portion, positioned in close proximity to the shoe portion of its complementary member to form a flux concentration gap between the shoe portions, a diverging portion connected to said shoe portion and directed away from said gap, a web portion connected to the diverging portion and positioned in widely spaced parallel relation to the web portion of its complementary member, and an extension portion connected to the web portion in a position normal to the web portion, said extension portion having a flat surface coplanar with the corresponding flat surface on its complimentary member;

individually contact the extension portions on the pole members, to a position where each pole extension contacts both of the extension portions of the pole members. 5 4. A permanent magnet erase head comprising:

pair of complementary pole members of magnetic material each comprising:

a ShOe portion, positioned in close proximity to the shoe portion of its complementary member to form a flux concentration gap between the shoe portions, a diverging portion connected to said shoe portion and directed away from said gap, a web portion connected to the diverging portion and positioned in widely spaced parallel relation to the web portion of its complementary member, and an extension portion connected to the Web portion in a position normal to the web portion, said extension portion having a fiat surface coplanar with the corresponding flat surface on its complementary member;

a cylindrically shaped permanent magnet slotted parallel to its axis to provide discrete segmental pole extensions of opposite polarity terminating in fiat surfaces in contact with the said fiat surfaces on the pole members, and said pole extensions being spaced apart substantially the same distance as the web portions of the pole members; and

means for supporting said permanent magnet for rotation from a position where the pole extensions on it individually contact the extension portions on the pole members, to a position where each pole extension contacts both of the extension portions of the pole members.

5. A permanent magnet erase head for magnetizing the magnetziable traces on a magnetic recording medium in a predetermined direction comprising:

a pair of pole shoes relatively closely spaced to form a flux concentrating gap between them adjacent the path of a magnetic recording medium;

flux conducting extensions formed integrally with said pole shoes and spaced relatively widely to form magnet contacting surfaces which are appreciably farther apart than the gap defining pole shoes;

a permanent magnet having pole extensions of opposite polarity for engagement with said magnet contacting surfaces, said pole extensions being spaced apart the same distance as the flux conducting extensions and being wide enough to span said flux conducting extensions; and

means for supporting said permanent magnet for rotation from a position where its pole extensions individually engage the flux conducting extensions and thereby complete a magnetic circuit across the flux pole extensions engage both of the flux conducting extensions to shunt magnetic flux from the fiux concentrating gap.

References Cited UNITED STATES PATENTS 9/ 1949 Camras 179-1002 X 6/1955 Steinegger l79100.2 1/1965 Steingroever 335302 BERNARD A. GILH-EANY, Primary Examiner.

G. HARRIS, Assistant Examiner.

concentrating gap, to a position where both of its 

1. A PERMANENT MAGNET ERASE HEAD FOR MAGNETIC RECORDING SYSTEMS COMPRISING: A PAIR OF POLE SHOES OF MAGNETIC MATERIAL; MEANS FOR SUPPORTING SAID POLE SHOES IN CLOSELY SPACED JUXTAPOSITION TO FORM A FLUX CONCENTRATING GAP BETWEEN THEM ADJACENT THE PATH OF MOVEMENT OF A MAGNETIC RECORDING MEDIUM; EXTENSIONS ON SAID POLE SHOES SPACED AN APPRECIABLY GREATER DISTANCE THAN THE WIDTH OF THE FLUX CONCENTRATING GAP; A PERMANENT MAGNET HAVING POLE EXTENSIONS OF OPPOSITE POLARITY SPACED SUBSTANTIALLY THE SAME DISTANCE APART AS THE SPACING OF THE POLE SHOE EXTENSIONS; AND MEANS FOR SUPPORTING SAID PERMANENT MAGNET FOR ROTATION FROM A POSITION WHERE ITS POLE EXTENSIONS WILL INDIVIDUALLY ENGAGE THE POLE SHOE EXTENSIONS TO GENERATE A FLUX FIELD AT THE POLE SHOE GAP, TO A POSITION WHERE BOTH OF ITS POLE EXTENSIONS WILL BRIDGE THE POLE SHOE EXTENSIONS AND SHUNT THE MAGNETIC FIELD AT THE GAP. 